1. Field of the Invention
The present invention relates to a hydraulic circuit for construction equipment, which can supply hydraulic fluid from a hydraulic pump to a working device through a confluence switching valve when switching valves for a traveling device and a working device, such as a boom, an arm, or the like, are shifted in a hydraulic system in which a plurality of hydraulic pumps are used.
More particularly, the present invention relates to a hydraulic circuit for construction equipment, which can prevent an abrupt operation of a working device, such as a swing device or an option device, when a switching valve for the corresponding working device is shifted in a state that a confluence switching valve has been shifted, i.e., in a state that switching valves for a traveling device and a working device have been shifted.
2. Description of the Prior Art
Generally, in a hydraulic circuit for construction equipment such as an excavator, at least one hydraulic pump and a confluence circuit are installed to supply hydraulic fluid from the hydraulic pump to a traveling device and a working device. Accordingly, when the working device except for the traveling device is driven, hydraulic fluid in the hydraulic pump is supplied to the working device through the confluence circuit to secure a smooth operation of the working device.
Referring to FIGS. 1 and 2, a conventional hydraulic circuit for construction equipment includes first to fourth hydraulic pumps P1, P2, P3, and P4 connected to an engine; first switching valves 1 and 2 composed of valves installed in a flow path of the first hydraulic pump P1 and shifted to control hydraulic fluid fed to working devices, such as a boom, an arm, and the like; second switching valves 5 and 6 composed of valves installed in a flow path of the second hydraulic pump P2 and shifted to control hydraulic fluid fed to the working devices; third switching valves 7 and 8 composed of valves installed in a flow path of the third hydraulic pump P3 and shifted to control hydraulic fluid fed to a swing device; fourth switching valves 3 and 4 composed of valves installed on upstream sides of the flow paths of the first and second hydraulic pumps P1 and P2, respectively, and shifted to control hydraulic fluid fed to left and right traveling devices; and a confluence switching valve 9 installed on a downstream side of the flow path of the third hydraulic pump P3 and shifted to supply the hydraulic fluid from the third hydraulic pump P3 to the working devices on the first hydraulic pump side P1 through a first confluence line 12 and to the working devices on the second hydraulic pump side P2 through a second confluence line 13, in response to a pilot signal pressure formed in a signal line 17 connected to the fourth hydraulic pump P4.
In order to form a signal pressure in the signal line 17, first and second throttling parts 19 and 20 are installed in the flow path of the fourth hydraulic pump P4. A signal line 15 for the traveling device connected to the signal line 17 is connected to a hydraulic tank through the fourth switching valves 3 and 4 for the traveling devices, and is connected to one side of a first valve 21.
A signal line 16 for the working device, which forms a signal pressure in the signal line, is connected to the signal line 17 on the downstream side of the second throttling part 20, is connected to the hydraulic tank through the first and second switching valves 1, 2, 5, and 6 for the working devices of the first and second hydraulic pumps P1 and P2, and is connected to the other side of the first valve 21.
In a traveling mode, the hydraulic fluid from the first hydraulic pump P1 is supplied to a right traveling motor by the shifting of the fourth switching valve 3, and the hydraulic fluid from the second hydraulic pump P2 is supplied to a left traveling motor by the shifting of the fourth switching valve 4.
In the signal line 15 for the traveling device that is blocked when the fourth switching valves 3 and 4 are shifted, a signal pressure is formed by the first throttling part 19. Accordingly, the first valve 21 is shifted in the right direction as shown in the drawing (at this time, the signal line 16 and the tank line 18 are blocked). If the first and second switching valves 1, 2, 5, and 6 for the working devices connected to the first and second hydraulic pumps P1 and P2 are not shifted, the signal pressure is not formed in the signal line 16 for the working devices.
That is, the signal pressure is not formed in the signal line 17, and thus the confluence switching valve 9 is not shifted, but is kept in its initial state.
When the fourth switching valves 3 and 4 for the traveling devices are shifted and a part of the switching valves 1, 2, 5, and 6 for the working devices is shifted, signal pressure is formed in the signal lines 15 and 16 by the first and second throttling parts 19 and 20. Accordingly, the confluence switching valve 9 is shifted in the right direction, as shown in the drawing, by the signal pressure formed in the signal line 17.
When the confluence switching valve 9 is shifted, a part of the hydraulic fluid from the third hydraulic pump P3 joins the working devices such as a boom, an arm, and the like, on the first hydraulic pump side P1 through the first confluence line 12. Also, a part of the hydraulic fluid from the third hydraulic fluid P3 joins the working devices on the second hydraulic pump side P2 through the second confluence line 13.
Accordingly, even in the case of driving the working devices during traveling, the working devices can be operated at a specified speed as the straight traveling is secured.
In the conventional hydraulic circuit, by shifting the fourth switching valves 3 and 4 for the traveling devices and at least one of the first and second switching valves 1, 2, 5, and 6 for the working devices, the confluence switching valve 9 is shifted by the signal pressure formed in the signal line 17. Accordingly, the hydraulic fluid from the third hydraulic pump P3 joins the first and second confluence lines 12 and 13.
If a center bypass 11 of the third hydraulic pump P3 is not connected to the tank line, a load pressure corresponding to the first and second switching valves 1, 2, 5, and 6 is formed in the center bypass 11.
Accordingly, in the case of shifting the third switching valves 7 and 8 connected to the third hydraulic pump P3, the working devices, such as a swing device, an option device, and the like, connected to the third switching valves 7 and 8 operates sensitively (i.e., abruptly operates), and thus the manipulation and safety of the working devices are lowered.